I've seen a lot of discussion on disclosing vs. not disclosing, but after reading through a few acceptance spreadsheets I noticed people also categorize their character and fitness issues into minor or major.

After skimming through a couple pages of the forums I couldn't really find anything which clearly delineates major from minor offenses. Is it as simple as whether one has a record with their school vs. with the police (assuming the school issue pertains to non-sexual related offences) or do other factors matter such as arrest vs. conviction in categorizing the offense as minor vs. major.

I was arrested four years ago for possession of marijuana (misdemeanor) but the prosecutor decided not to press charges and I simply walked out most likely due to plea bargaining (rather than on account of some legal technicality/my lawyer was never very clear on what happened), not certain how to phrase that on my application without coming off as obnoxious or whether I should be looking at minor vs. major C&F on the spreadsheets to see which general scores and C&F situation most closely corresponded to mine.

You don't need to overthink your C&F disclosures for law school admissions. First, you'll want to read the prompt on C&F for each school before tailoring your response. Some look for any violations to include traffic violations and speeding, while others are much more specific about the types of offenses they consider a required disclosure.

As for your specific situation, you just need to disclose the facts once you accurately figure out what they are. Check with the court house for your record so you know what is in it and what the final disposition of your case was (if you don't have the court documents readily available already, that is). And once you nail down exactly what happened, what you were charged with, and the final disposition of the case, tell them exactly that, followed by a brief statement of contrition, how you've learned from your mistakes, and haven't had any further legal issues since the last event.

Keep in mind, C&F disclosure for law schools is more to establish a record of consistency before you go before a state bar association, so disclosing everything accurately is really all that matters. They're also looking to ensure you'll one day be able to sit for the bar, but in your case, that doesn't sound like it'll be much of an issue. So just disclose everything you know and can find on your personal record.

It really depends on the school. I applied to 14 schools last cycle and some asked for just about everything, even down to parking tickets while others asked for nothing at all. I disclosed an incident I had back in 2011 to all schools that asked, but all I did was explain the situation and how it was taken care of. A short paragraph will suffice honestly. As far as not disclosing goes, I would not recommend it. I really don't think a minor incident like yours will have a detrimental impact on your chances of getting into a school, and you really don't want your chances of going to your dream school to go down the drain because you were too lazy to write one short paragraph explaining a situation that happened years ago.